Method for the characteristic map-based obtention of values for a control parameter of an installation

ABSTRACT

Disclosed is a method for the characteristic map-based obtention of values for at least one control parameter of an installation, particularly an internal combustion engine. According to the inventive method, support points for the control parameter, which provide a value for the control parameter, are defined across a range of operational parameters within a characteristic map ( 4 ) in accordance with operational parameters of the installation, the range of operational parameters covered in said characteristic map is divided into a first and a second subdomain which comprises several of the support points, and the value for the control parameter is obtained by extrapolation when a boundary of the first subdomain is reached before the value for the control parameter is obtained by accessing support points of the second subdomain.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a method for the characteristic map-basedobtention of values for at least one control parameter of aninstallation, particularly an internal combustion engine, wherebysupport points for the control parameter, which provide a value for thecontrol parameter, are defined across a range of operational parameterswithin a characteristic map in accordance with operational parameters ofthe installation.

For installations, in particular for internal combustion engines, it haslong been known to store control parameters in characteristic maps sothat an optimal value can be obtained for the control parameter for acurrent operating point according to the most varied input quantities,such as, for example, speed, load, operating temperature, oiltemperature.

For internal combustion engines that can be run in different discreteoperating modes, i.e. where one can choose between different operatingmodes, it is usual to have a characteristic map ready for each operatingmode, which map is specific to and optimized for the respective mode.Then when an operating mode is changed, there is a switch over to thecharacteristic map specific to the operating mode, so that thischaracteristic map will be accessed in the further operation of theinternal combustion engine, in any event as long as the assignedoperating mode continues. An example for such an operating mode changecan be found in internal combustion petrol engines, which can be run instoichiometric or various lean operating modes. Normally there are threeknown operating modes for such internal combustion engines, that is tosay, stoichiometric, uniform-lean and stratified-lean.

A further internal combustion engine type which allows several operatingmodes, are internal combustion diesel engines, whereby fuel is injectedfrom a high pressure reservoir (common-rail injection system). There,the fuel quantity injected for a work cycle can be distributedpractically at will into single (shot) injections. In this context, onetalks about pre, main and post injections. The flexibility of the designof an injection process effects very many different operating modes forsuch internal combustion engines, each modes being characterized by thedistribution of the fuel quantity per work cycle in the above mentionedinjections. As each operating mode must have its own characteristic mapheld ready, the memory requirement for operating control units ofinternal combustion engines of this type is greatly increased.Furthermore the application, i.e. the adaptation of an internalcombustion engine control structure to a current internal combustionengine model, becomes relatively complex with the plurality ofcharacteristic maps.

SUMMARY OF THE INVENTION

The object of the invention is therefore to provide a method for thecharacteristic map-based obtention of values for at least one controlparameter of an installation of the type cited above, whereby the memoryrequirement can be kept as low as possible even if there are manydifferent operating modes.

This task is achieved according to the invention by a method for thecharacteristic map-based obtention of values for at least one controlparameter of an installation, particularly an internal combustionengine, whereby support points for the control parameter, each of whichprovide a value for the control parameter, are defined across a range ofoperational parameters within a characteristic map in accordance withoperational parameters of the installation, the range of operationalparameters covered in said characteristic map is divided into a firstand a second subdomain which comprises several of the support points,and the value for the control parameter is obtained by extrapolationwhen a boundary of the first subdomain is reached before the value forthe control parameter is obtained by accessing support points of thesecond subdomain.

Thus the invention departs from the previous approach of providing aspecific characteristic map for each operating mode and instead usessubdomains in characteristic maps. As a change from one subdomain to thenext corresponds in prior art to the switching between individualcharacteristic maps, but regularly involves a non continuous change inthe value of the control parameter, which change is, it is not possibleto simply change from one subdomain to the next, as that would result ina jump. When operating at the boundary of the subdomain, this would leadto continual jumps, this being incompatible with smooth control of theinstallations.

A hysteresis is achieved by means of the extrapolation according to theinvention across the subdomain, which nevertheless results in acontinuous, uniform and fault free installation operation despite thetransition of the control parameter values at the subdomain boundariesnot being constant, even when there are operating points at boundariesof subdomains over a longer period of time. The obtention of values forthe control parameter within the subdomains is carried out by thestandard method, i.e. by evaluating the support points and possiblysuitable interpolation.

Thus the invention carries out a standard interpolation between supportpoints within a subdomain, and in the case of support points atsubdomain boundaries, i.e. in the case of support points that areadjacent to other subdomains, the invention carries out an extrapolationbased on that support point. By means of the extrapolation, thetransitions between the subdomains are cleanly separated and at the sametime a memory, in which the characteristic map is held ready, isoptimally utilized.

The hysteresis provided for the transition between the two subdomains isin principle already achieved by the fact that an extrapolation occursstarting from a subdomain. A particularly large hysteresis, and henceone resulting in stable operating behavior of the installation, isachieved, however, by effecting an initial extrapolation also after achange of subdomain. It is therefore preferable that when a certaindistance from the last support point of the first subdomain is reached,the value is obtained by extrapolation from support points of the secondsubdomain.

In principle the number of subdomains can be chosen at will, a personskilled in the art will select this in accordance with the operatingbehavior of the installation. It is particularly preferable for internalcombustion engines in particular, that a (discrete) operating mode ofthe installation is assigned to each subdomain. A one-to-onecorrespondence between subdomain and operating mode then makes itpossible for a single characteristic map to suffice for all operatingmodes of the installation.

The method according to the invention is especially advantageous withthe internal combustion engine type mentioned above, in which enginefuel is injected directly into combustion chambers and the discreteoperating modes are differentiated by the number of injections per workcycle. The internal combustion diesel engines mentioned that have directinjection from high pressure reservoirs provide an example of suchinternal combustion engines.

In the case of internal combustion engines with direct injection, thequantity of fuel that is introduced into the combustion chambers withthe main injection is an important parameter for controlling theoperation of the internal combustion engine. A further injectionparameter is the time of the injection. Therefore, it is especiallypreferred that the characteristic map contains values of injectionparameters in accordance with speed and load of the internal combustionengine, whereby the injection parameters can include injection quantityand/or injection angle.

The 1:1 assignment mentioned, between subdomains of the characteristicmap and operating modes of the internal combustion engine, has theadvantage that an application, i.e. an adaptation of a control structureto an internal combustion engine model, is especially simple. It thenpossible to control the internal combustion engine in such a way thatwhen the stated specific operating state is reached, i.e. when aboundary of a subdomain is reached, simultaneously a change of theoperating mode is carried out. Then, the subdomain of the characteristicmap which is assigned to the respective operating mode is alwaysaccessed in order to obtain the values of the at least one controlparameter.

The invention is described in more detail below with reference to thedrawing by way of example in which;

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an internal combustion diesel enginewith high pressure reservoir injection,

FIGS. 2-5 shows time sequences of the process of an injection for a workcycle of a cylinder in an internal combustion engine of FIG. 1,

FIG. 6 shows a schematic representation of a characteristic map for theoperation of the internal combustion engine in FIG. 1,

FIG. 7 a flow chart for the obtention of control parameter values in theinternal combustion engine in FIG. 1,

FIG. 8 a model cycle through the characteristic map in FIG. 6 in anoperational phase at a constant speed and

FIG. 9 the values for a control parameter obtained during the cycle inFIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a schematic representation of an internal combustion engine1, which has a injection system 2, which injects the fuel directly intothe combustion chambers of the internal combustion engine 1 via (notshown in detail) lines and injectors. The injection system 2 has a highpressure accumulator, which feeds injectors leading into the combustionchambers of the internal combustion engine 1. These injectors of theinjection system 2 can be controlled independently of the rotationalposition of a crankshaft of the internal combustion engine 1, so that itis possible to freely control the injection discharge rate from the highpressure accumulators.

A control device 3 controls both the internal combustion engine 1 andthe injection system 2, said control device being connected to theseunits via lines (not shown in detail). The control device 3 has acharacteristic map 4 and a control core 5, which control the operationof the internal combustion engine. Values for the duration of injectionas function of the speed and load of the internal combustion engine arestored in the characteristic map 4 (which is detailed further later),the characteristic map having several support points, each of whichprovide a value for the injection quantity for a specific combination ofload/speed.

The control device 3 naturally has other characteristic maps and controlelements, which are, however, of no further relevance for the followingdescription for the characteristic map-based obtention of values for acontrol parameter.

The control device 3 controls the injection system with respect to theduration the injectors are active. Thereby, as already mentioned,different injection discharge rates can be set for a work cycle. Forexample, the control device 3 of the internal combustion engine 1 canrealize the injection discharge rates illustrated in FIGS. 2 to 5. InFIGS. 2 to 5, a fuel quantity rate MF over the time t is illustrated ineach injection discharge rate 6.

FIG. 2 shows a first operating mode M1, in which the injectors onlydeliver one main injection 7. Thereby, a fuel quantity 8 of the maininjection 7 results from the integration of the fuel quantity rate MFover the time t of the main injection 7.

FIG. 3 shows another mode M2, which differs from the mode M1 in the factthat the main injection 7 precedes a pre-injector 9. Thereby, in themain injection 7 the fuel quantity 8 is delivered, and a fuel quantity10 is delivered by the pre-injector 9. Normally, such pre-injectors areused to make combustion proceed “softly” and to reduce the operatingnoise of an internal combustion engine.

A further reduction in noise is produced in a mode M3, illustrated inFIG. 4. Here an additional pre-injector 11 precedes the pre-injector 9,and said pre-injector 11 injects a fuel quantity 12 into the combustionchamber. Otherwise mode M3 corresponds to mode M2.

The great flexibility that the injection system supplied from a pressurereservoir allows is shown in FIG. 5 in which a further mode M4 isillustrated. In this mode, in addition to the main injection 7, whichfeeds the fuel quantity 8 into the combustion chamber, and to thepre-injector 9, which contains the fuel quantity 10, a post injector 13with a fuel quantity 14 is delivered after the main injection 7. Usingsuch a post injector produces an increase in torque at low speeds.

As can be clearly seen, in the operation of the internal combustionengine 1, only one of the modes M1 to M4 can be executed at a time. Thecontrol device 3 therefore effects an appropriate mode switch, which istriggered by control core 5, which has recourse to the characteristicmap 4 and ensures that the internal combustion engine 1 is alwaysrunning in the most appropriate operating mode M1 to M4. Thereby, thecontrol core 5 accesses the characteristic map 4, schematicallyrepresented in FIG. 6, in order to select or determine the fuel quantity8 of the main injection 7.

FIG. 6 shows the basis of the characteristic map 4, which extends overthe speed N and the torque TQI. The shaded areas of the characteristicmap 4 contain support points, each of which provides a value for thefuel quantity 8. In a three dimensional interpretation of thecharacteristic map 4 the support points would be vectors runningperpendicular to the plane of projection, the length of which vectorsspecifies the fuel quantity 8. Thereby, the support points (not drawn inFIG. 6) are distributed across the shaded areas of the characteristicmap 4, the distribution being normally, though not necessarily,equidistant. Thus a higher support point density can be planned forcertain operational areas, in particular where speeds are low.

The characteristic map 4 has four subdomains T1 to T4, which areallocated to the respective operating modes M1 to M4. The diagrammaticview in FIG. 6 differentiates the subdomains by the shading. Thesubdomains border on each other in transition areas 15 to 18, wherebythe transition area 15 separates the subdomains T2 and T3 (correspondingto the modes M2 and M3), the transition area 16 separates the subdomainsT2 and T4 (corresponding to the modes M2 and M4), the transition area 17separates the subdomains T3 and T4 (corresponding to the modes M3 andM4) and the transition area 18 separates the subdomains T1 and T2(corresponding to the modes M1 and M2) from each other. There are nosupport points in the transition areas 15 to 18, which are symbolized bythicker black lines in FIG. 6.

To achieve a smooth running of the internal combustion engine when theinternal combustion engine 1 is operated near or in the vicinity of oneof the transition areas 15 to 18, the transition areas 15 to 18 are usedto execute a hysteresis, as represented in FIG. 7 as a flow chart.

First in a step S0, the internal combustion engine is started withdefined subdomain and defined mode, for example, subdomain T3 and modeM3. The values for the fuel quantity 8 are then obtained within thissubdomain by an interpolation between the support points; this occurs instep S1. By interpolation it is also understood, of course, that in theevent that speed N and torque TQI are exactly at a support point,exactly the value supplied by the support point is used for the fuelquantity 8. Thereby, the internal combustion engine is operated in theoperating mode M3, i.e. two pre-injectors 9 and 11 are executed and themain injection 7 lasts so long that the fuel quantity supplied by thesubdomain T3 of the characteristic map 4 is delivered by the fuelquantity 8.

After each obtention of a value for the fuel quantity 8, in a step S2 itis queried whether the operating point is in a transition area. Thisquery can be carried out by checking whether there is a further supportpoint within the subdomain for the active mode, beyond the currentoperating point, i.e. in the direction in which the dynamic of theoperation of the internal combustion engine indicates a development ofspeed N and torque TQI. If this is not the case, there is an operationin the transition area. If there is no transition area (N branch) then ajump back is made before step S1.

If, on the other hand, there is a transition area (J branch) step S3 iscontinued with, in which step there now occurs an extrapolation withrecourse to the support points of the subdomain T3 to find the value forthe fuel quantity 8 of the main injection 7.

After each extrapolation, a step S4 queries whether a hysteresisdistance H exceeds a threshold value SW. In this way a check is made asto whether the distance from the last support point of the activesubdomain, which is valid for the current mode, exceeds the thresholdvalue SW, i.e. it is checked whether there is (still) an operation inthe transition area. If this is not the case (N branch) a jump back ismade before step S2.

Nevertheless if the hysteresis distance H has exceeded the thresholdvalue SW, i.e. if a certain minimum distance from the nearest supportpoint of the active subdomain is reached, then step S5 (J branch) iscontinued with, said step effecting a change of the operating mode.Thereby, the change occurs into the mode which has the nearest supportpoint in relation to speed N and torque TQI. Exceeding the thresholdvalue of the hysteresis distance H, thereby ensures that this querydelivers an unequivocal result and hence the determination of theoperating mode now to be used.

After the operating mode and thus also the relevant subdomain waschanged in step S5, step S1 comes in again, i.e. the determination ofthe fuel quantity 8 is made again by interpolation in the now currentsubdomain of the characteristic map 4. If an interpolation is notpossible, an extrapolation can possibly also be carried out analogouslyto step S3.

The choice of the threshold value SW for the hysteresis distance Hensures that, in any case, support points of the now current subdomainare closer than those of the subdomain that has just been left.

FIGS. 8 and 9 show the process described using FIG. 7 again and ingreater detail. FIG. 8 thereby shows a section from the characteristicmap 4 in FIG. 6 and shows the passage through two operating mode changesat a constant speed. The graph in FIG. 9 shows the associated fuelquantity 8 as a function of the torque TQI.

Operating points B1 to B9 are drawn in FIG. 8 and FIG. 9 shows thecorresponding data points D1, D2, E3 a, E3 b, D4, D5, D6, E7 a, E7 b, D8and D9 which are allocated to said points. The data points marked with Dare values obtained by interpolation from the characteristic map 4 or asubdomain of the characteristic map 4, the data points marked with E arevalues obtained by extrapolations.

In the process illustrated in FIGS. 8 and 9, the internal combustionengine 1 is first operated in an operating point B1. For reasons ofsimplicity, a constant speed will be assumed for the following operatingpoint change. By increasing the torque TQI or the requirement for thistorque, the internal combustion engine reaches the operating point B2,which, like the operating point B1 is handled in the mode M3, in whichthe subdomain T3 is accessed. The data point D2 is obtained for theoperating point B2 from the subdomain T3 of the characteristic map 4 byinterpolation.

By dint of a further torque increase, the internal combustion enginereaches the operating point B3, which now lies in the transition area15. Thus now (for the first time) the query in step S2 leads to the Jbranch. From now on, the fuel quantity 8 is obtained by extrapolation,and hence there is an extrapolated data point E3 a in FIG. 9. Furtherdevelopment of the torque TQI results in the hysteresis distance Hexceeding the threshold value SW, which is why mode change 19 is carriedout, and the internal combustion engine subsequently runs in operatingmode M2. Thus the additional pre-injector 11 will no longer bedelivered.

In operating mode M2, the obtention of the value for the fuel quantity 8is made by extrapolation with recourse to the values of the subdomain T2of the characteristic map, so that now an extrapolated data point E3 bprovides the value for the fuel quantity 8 in the operating mode M2. Thetorque increases further and brings the internal combustion engine tothe operating point B4, for which a read-out data point D4 gives thevalue for the fuel quantity 8 of the main injection 7, and possibly doesso by interpolation.

In subsequent torque increases, operating points B5 and B6 are reachedin operating mode M2, and (read-out) data points D5 and D6 are allocatedto said operating points. The torque TQI continues to rise, this resultsin an operating point B7, which operating point is in a transition area,in this case in the transition area 16. Here the description given forthe transition area 15 applies analogously, i.e. the next value for thefuel quantity 8 is obtained by extrapolation at a data point E7 a,whereby the support points of the subdomain T2, which is allocated tothe operating mode M2, are used for the extrapolation.

In the moment in which the hysteresis distance exceeds the thresholdvalue (J branch of step S4), there is a mode change 20, and when theinternal combustion engine is operated in mode M4, now in addition postinjector 13 is delivered. The valid fuel quantity 8 of the maininjection 7 for this operating mode is obtained from subdomain T4 byextrapolation, so that there is an extrapolated data point E7 b. Furthertorque increases bring the internal combustion engine to operatingpoints B8 and B9, at which the value for the fuel quantity 8 is obtainedusing data points D8 and D9.

1. A method for obtaining, on the basis of a characteristic map, a valuefor at least one control parameter of an installation, the method whichcomprises: defining support points for the control parameter, each ofthe support points providing a value for the control parameter, across arange of operational parameters within a characteristic map inaccordance with operational parameters of the installation; dividing therange of operational parameters covered in the characteristic map intofirst and second subdomains each comprising a plurality of the supportpoints; storing the characteristic map in a control device that controlsthe installation; using the control device to obtain a value for thecontrol parameter by extrapolating when a boundary of the firstsubdomain is reached before the value for the control parameter isobtained by accessing support points of the second subdomain; andwherein the control device uses the control parameter to control theinstallation.
 2. The method according to claim 1, wherein the controlparameter is a control parameter of an internal combustion engine. 3.The method according to claim 1, which comprises, when a given distanceis reached from a last support point of the first subdomain, obtainingthe value by extrapolating from support points of the second subdomain.4. The method according to claim 1, which comprises using the controldevice to allocate a discrete operating mode of the installation to eachsubdomain.
 5. The method according to claim 4, which comprises using thecontrol device to change an operating mode of the installation when agiven operating state is reached.
 6. The method according to claim 4,wherein the installation is an internal combustion engine having fuelinjected into combustion chambers, and the method comprises defining thediscrete operating modes as differing in a number of injections per workcycle.
 7. The method according to claim 6, wherein the characteristicmap contains values of injection parameters in dependence on a speed anda load of the internal combustion engine.
 8. The method according toclaim 7, wherein the injection parameters include at least one of aninjection quantity and an injection angle.